Mud volcanoes represent the largest expression of natural methane release into the atmosphere; however, the gas flux has never been investigated in detail. Methane output from vents and diffuse soil degassing is herewith reported for the first time. Measurements were carried out at 5 mud volcano fields around Sicily (Italy). Each mud volcano is characterized by tens of vents and bubbling pools. In the quiescent phase, methane emission from single vents ranges between 0.01 and 6.8 kg/day. Diffuse soil leakage around the vents is in the order of 102--104 mg m-2 d-1. An exceptional flux of 106 mg m-2 d-1 was recorded close to an everlasting fire. Soil CH4 flux is positive even at large distances from the mud volcano fields suggesting a diffuse microseepage over wider areas. A total of at least 400 tons CH4 per year can be estimated over the area investigated alone (~1.5 km2).